A thick film resistor composition widely used in thick film resistor electrical parts, thick film hybrid circuits, etc. is a composition for forming a resistor thick film by printing the composition on a conductor pattern or an electrode formed on the surface of an insulating substrate, and then firing the print.
The thick film resistor composition is prepared by dispersing a conducting component and a glass binder in an organic medium (vehicle). The conducting component plays a principal role of determining the electrical properties of the thick film resistor, and a ruthenium pyrochlore oxide or the like is used as the conducting component. The glass binder consists of glass, and has a major role of retaining the thick film integrally and binding it to the substrate. The organic medium is a dispersing medium that affects the application properties, particularly rheology, of the composition.
Ruthenium pyrochlore oxide series thick film resistors containing ruthenium pyrochlore oxides such as lead ruthenate (PbRuO.sub.3) are usually fired by means of a belt furnace. In this case, the substrates with prints of the resistor compositions to be fired are arranged on the belt of the belt furnace, and heated for firing. Generally, the firing is performed at a peak temperature of 850.degree. C. for a peak time of 5-10 minutes. The travel from the inlet to the outlet of the belt furnace takes about 25-110 minutes, but the firing time becomes shorter year by year. As the belt speed increases, however, the resistance and the temperature coefficient of resistance (TCR) of the fired resistor fluctuate, and their variations increase. Some variation in the resistance can be corrected by a subsequent laser trimming step, while TCR cannot be adjusted. Thus, it is desired to minimize its fluctuations and variations due to the firing.
It is also important for the ruthenium pyrochlore oxide series resistor to have a small thermal coefficient of expansion (TCE). Since 96% alumina ceramic, an ordinary substrate, has a TCE of 75.times.10.sup.-7 /.degree.C., the TCE of the thick film resistor should preferably be smaller than that.